Next Generation Networks are large, complex and heterogeneous structures and the relative control plane should automatically and dynamically provide end-to-end connections spanning domains, technology regions and layers.
The main standardization bodies (IETF, OIF and ITU) are addressing several aspects of routing in a multi-domain/multi-technologies scenario, where a single domain can also be multi-layer (i.e. a Wavelength-Switched Optical Network, WSON, domain with packet interfaces at its borders). The common approach followed for multi-layer, multi-technology and multi-domain networks is mainly based on the division of the network resources into “technology regions” (e.g. optical and packet regions), having hierarchical server-client relations. On such architecture, the Generalised Multiprotocol Label Switching, GMPLS, protocol suite, with the relative extensions for each technology and layer, should allow a homogeneous control of portions of the network, which are heterogeneous both technologically and administratively.
The large amount of network elements and their management complexity imply a set of scalability issues both for routing and for signaling protocols. As a matter of fact, the amount of information to be distributed and the frequency of updates increase the overhead of the entire network signaling and thus the bandwidth request and the computational power consumed. On the other hand, poor information (e.g. Traffic Engineering, TE, information not transmitted from one hierarchical layer to another one or a too generic resource virtualization) can lead to an inefficient resources utilization and to a high blocking probability (i.e. the probability that a connection seen as feasible at a higher hierarchical level can not be provided, because of a lack of resources in the lower level).
Moreover, different domains can be administrated by different carriers as well, resulting in a set of confidentiality issues due to strong commercial reasons that refrains a domain administrator to disclose all the details of its intra domain topology.
However a common view of these complex topics has not been proposed so far and a set of issues are still to be fixed.
As a first step for providing a framework for hierarchical architectures with resources' summarization a patent application WO2011/103913A1 has been filed, defining a general hierarchical architecture with service-oriented parameters. This patent application addresses the issue of defining a general architecture and a common set of parameters, but it does not specify any method to perform resource summarization.
In order to fix the scalability issue in multi-region and multi-carrier scenarios, the design of hierarchical architectures, based on Path Computation Elements (PCEs), seems to be a promising approach, currently under standardization.
However, such approach is not completely defined and technology-specific extensions are still needed. Moreover, End-To-End, E2E, path computation procedures should be further improved and extended in order to work efficiently also on summarized topologies.
Concerning the topology summarization concept itself, a set of guidelines are expressed in the standards, but they only indicate that a domain can be summarized as a single node, as a full mesh of links interconnecting some border nodes, or some generic intermediate solution. Moreover, the domain summarization is actually mainly considered as an enabler for preliminary considerations such as the domains' chain definition, not exploiting its real potential.
Another important lack of the existing solutions is that, for both PCE hierarchical architectures and domains summarization, standards only provide guidelines and general approaches. As a matter of fact, there is no common view with any specific solutions or defined framework addressing all the issues of Multi-Layer, Multi-Region, Multi-Vendor and Multi-Domain Networks.
As mentioned in the previous section, the patent application WO2011/103913A1 has been filed as a first step for providing a framework for hierarchical architectures with resources summarization. It describes a general hierarchical architecture to summarize domain topologies in a multi-domain and multi-technology context to be used for E2E solutions. Main concepts of WO2011/103913A1 are:                Architectural definition of specialized PCEs, summarizing the intra-domain topologies, and inter-domain external PCE, working on a summarized view of the topologies.        Definition of service-based parameters to be used for the summarization of each domain, acting as “umbrella” parameters for different technologies.        
WO2011/103913A1 addresses the issue of defining a general architecture and a common set of parameters; however it does not specify any method to perform an efficient resource summarization.